San Bruno Mountain rises to 1,319 feet directly from the edge of San Francisco Bay, a geological anomaly called a fault-block horst, pushed upward by the same tectonic forces that created the San Andreas Fault. The mountain straddles the boundary between San Francisco and San Mateo counties, and its summit is the highest point on the northern peninsula. From the top, on a clear day, you can see from Mount Tamalpais to Mount Diablo to the Farallon Islands. The mountain's grasslands and coastal scrub support several endangered species, including the Mission blue butterfly, which survives here and almost nowhere else.
San Bruno Mountain is a horst, a block of crust pushed upward between two parallel faults. The mountain's exposed ridgeline and steep slopes create a range of microclimates and habitats that are unusually diverse for such a small area. Coastal scrub, grassland, and riparian corridors support plant and animal communities that have been squeezed out of the surrounding urbanized landscape. The mountain functions as an ecological island, surrounded by development on all sides. The Mission blue butterfly, listed as federally endangered in 1976, depends on lupine plants that grow on the mountain's slopes. The San Bruno elfin butterfly and several rare plant species are also found here.
In the 1960s and 1970s, developers proposed covering much of San Bruno Mountain with housing. Environmental groups fought to preserve the mountain, and the resulting compromise produced the San Bruno Mountain Habitat Conservation Plan in 1982, the first such plan in the United States under the Endangered Species Act. The plan allowed limited development on the lower slopes while preserving the ridgeline and upper elevations as open space. The precedent set here influenced habitat conservation planning nationwide. San Bruno Mountain State and County Park now protects approximately 2,326 acres, including the summit and the main ridgeline.
The summit trail offers some of the most expansive views in the Bay Area. On clear days, the panorama extends from the Golden Gate Bridge to the Santa Cruz Mountains. The wind on the ridgeline can be fierce, bending the coastal scrub into permanent leans. A hidden trail leads to the April 25th memorial, commemorating the victims of the 1915 Armenian genocide. The mountain's north face drops steeply toward Bayshore, where residential neighborhoods press against the park boundary. San Bruno Mountain is the kind of place that reminds you San Francisco sits on the edge of the wild, not in the middle of it. The city ends. The mountain begins.
Located at 37.69°N, 122.43°W on the San Francisco Peninsula, rising to 1,319 feet. The mountain ridge is clearly visible from altitude between San Francisco and Daly City/South San Francisco. Nearest airports: SFO (KSFO, 4 nm south), Oakland (KOAK, 11 nm east). The summit exceeds 1,300 ft MSL.